This invention relates generally to devices for implementing a ground connection between a metallic shield of a cable and a common ground point. More particularly, the present invention relates to devices which mount to fiber optic cables and implement a ground connection via a flexible conductor.
Fiber optic cables are generally buried under ground and typically constructed in a tubular fashion with numerous fiber optic conductors surrounded by a conductive ground shield which is in turn surrounded by a protective jacket of tough flexible plastic or rubber. Many fiber optic cables also include steel cords running the length of the cable, positioned between the conductive shield and the protective jacket, which protect the fragile inner conductors and reinforce the cable. To function properly and safely, cable shields must be grounded at spaced ground points established by regulation and/or operational specifications and practices.
Cable shield ground assemblies are ordinarily positioned within a cabinet, housing or other enclosure to provide a common ground point and shelter for the cables and attached grounding assemblies. Such enclosures are frequently located outdoors and/or underground, where the enclosures and their contents are subjected to intense environmental changes. It is not uncommon for the enclosure to be exposed to moisture in the form of rain, ground water or condensation. Temperature swings from well below freezing to above 100xc2x0 F. are not uncommon.
Establishing reliable electrical connections between the conductive shield of fiber optic cables and a common ground point presents difficulties well known in the art. Conventionally, craft personnel must cut through the protective jacket and expose the metallic shield prior to affixing any clamp or other device for establishing a ground path. Any such cutting or piercing of the protective shield by craft personnel makes the fiber optic conductors and linear strength members susceptible to being damaged, weakened or cut with the potential for delays and costly repairs. Costs are further increased by the specialized training and equipment required to prepare craft personnel to perform the task of cutting the cable shield.
Briefly stated, the invention in a preferred form is a fiber optic cable shield bond system for establishing a reliable ground path from the conductive shield of a fiber optic cable to a common ground point via a flexible conductor. A preferred form of the fiber optic cable shield bond system includes a cable shield connector having a rigid, electrically conductive bond plate which is mounted to the fiber optic cable by at least one hose clamp. At least one ground connector in electrical communication with the bond plate penetrates the protective jacket of the fiber optic cable to electrically connect the bond plate to the cable shield. A harness assembly mounted to the bond plate may be connected to a ground point and thereby ground the conductive shield of the fiber optic cable.
The bond plate includes first and second side portions forming an obtuse angle therebetween and defining a longitudinal channel with open ends. The bond plate also includes first and second end portions and a middle portion disposed longitudinally therebetween. The first side portion of the bond plate has at least one threaded opening and the second side portion has a threaded opening and an unthreaded guide hole, the threaded openings being disposed in the middle portion of the bond plate.
The ground connector comprises a grounding screw including a driving head, a threaded shank axially extending from the head and terminating in a cutting edge which forms the extreme distal tip of said grounding screw. One of the grounding screws is threadably mounted within each of the threaded openings. The shank of the grounding screw has an axial recess extending from the distal tip to a point intermediate the distal tip and the driving head, the cutting edge forming a sharpened hollow point.
The harness assembly comprises a electrically conductive flexible cable and a electrically conductive, substantially rigid wire, with one end portion of the flexible cable being mounted to one end portion of the rigid wire. The other end portion of the flexible cable is mounted to the bond plate and the other end portion of the rigid wire may be mounted to the ground point.
To install the system, the bond plate is positioned adjacent the protective jacket of the fiber optic cable and at least one of the end portions of the bond plate is clamped to the cable with a hose clamp. Each grounding screw is tightened until the cutting edge penetrates the protective jacket of the cable and makes electrical contact with the cable shield. The rigid wire is connected to the ground point to complete the ground circuit.
The bolt on each hose clamp has a break-away cap, the bolt is tightened until the break-away cap breaks off, ensuring that the proper amount of compressive force is applied to the bond plate and fiber optic cable. A drill bit having a hardness which is greater than the hardness of the protective jacket but less than the hardness of the conductive shield is inserted through the guide hole of the bond plate to engage the protective jacket. The drill bit is rotated to remove the protective jacket exposed by the guide hole, thereby forming an opening in the protective jacket.
One of the probes of a continuity test device is engaged with the hose clamp and the other probe is inserted through the guide hole and the opening in the protective jacket to contact the conductive shield. A first of the grounding screws is tightened until a reading is obtained on the continuity test device, indicating electrical contact between the grounding screw and the conductive shield. The first grounding screw is then backed-off until the continuity test device indicates that electrical contact has been broken. Each remaining grounding screw is initially engaged with the shield in the same manner. Each grounding screw is then tightened one half a turn, ensuring proper contact with the shield. The opening in the protective shield may then be sealed with a sealing material if desired.
An object of the invention is to provide a new and improved connector for establishing and maintaining a high quality ground connection with a fiber optic cable shield.
Another object of the invention is to provide a new and improved fiber optic cable shield bond system which does not require opening of the cable shield prior to installation.
A further object of the invention is to provide a new and improved fiber optic cable shield bond system that minimizes damage to the fiber optic cable jacket while establishing reliable grounding of the fiber optic cable shield.
A yet further object of the invention is to provide a new and improved fiber optic cable shield bond system which reduces labor costs and craft error.
A yet further object of the invention is to provide a new and improved fiber optic cable shield bond system having improved water, weather and environmental resisting capabilities.
Other objects and advantages of the invention will become apparent from the specification and the drawings.